1. Field of the Invention
The invention relates to a control device for a turbocharger with an electric motor, in which a compressor of the turbocharger can be driven by the electric motor, and a control method of same.
2. Description of the Related Art
An attempt has been made in order to obtain high-power (or high fuel efficiency) by supercharging air taken in an engine (i.e., internal combustion engine) using a turbocharger. It has been required that some improvements be made to the turbocharger. For example, a supercharging pressure rises slowly in a low rotational region, and an engine output characteristic is not good in the low rotational region. These problems occur in the low rotational region where an amount of exhaust energy is small, due to a configuration of the turbocharger in which the intake air is supercharged using the exhaust energy. In order to address these problems, twin turbo system is generally adopted. Meanwhile, an attempt is made in order to obtain a required supercharging pressure by embedding an electric motor (i.e., a motor) in a turbine/compressor and driving the turbine/compressor forcibly. In this case, it is possible to make the electric motor perform regenerative power generation using the exhaust energy. An example of such a turbocharger with an electric motor is disclosed in Japanese Patent Laid-Open Publication No. 4-164132.
In the turbocharger with an electric motor disclosed in Japanese Patent Laid-Open Publication No. 4-164132, an amount of assist performed by the electric motor (i.e., an amount of electric power to be supplied) is decided based on a difference between a target supercharging pressure and an actual supercharging pressure. However, when a high-power is needed immediately such as rapid acceleration time, control is performed based on the target supercharging pressure and the actual supercharging pressure, and the supercharging pressure is brought close to the required supercharging pressure according to the feedback of the control. Therefore, a time lag is caused before an effect of the assist by the electric motor is obtained. Accordingly, it has been desired that the responsiveness during rapid acceleration or the like be improved.